Theory of magnetic impurities in metals
01 Aug 1970-Vol. 11, Iss: 3, pp 255-278
TL;DR: In this article, the theory of magnetic impurities in metals is considered starting from the strong correlation or ionic limit as a zero-order approximation, and an appropriate model Hamiltonian is derived which includes collective intra-ionic structure and new kinds of mixing interactions between local and conduction electrons.
Abstract: The theory of magnetic impurities in metals is considered starting from the strong-correlation or ionic limit as a zero-order approximation. An appropriate model Hamiltonian is derived which includes collective intra-ionic structure and new kinds of mixing interactions between local and conduction electrons. The relation of the present approach to the Friedel-Anderson theory is discussed in some detail.
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TL;DR: In this article, the authors review the experimental results observed in the subset of rare-earth systems for which the 4f ions form a lattice with identical valence on each site, and discuss key thermodynamic experiments, such as susceptibility and lattice constant, and spectroscopic experiments such as XPS and neutron scattering.
Abstract: Valence fluctuation phenomena occur in rare-earth compounds in which the proximity of the 4f level to the Fermi energy leads to instabilities of the charge configuration (valence) and/or of the magnetic moment. The authors review the experimental results observed in the subset of such systems for which the 4f ions form a lattice with identical valence on each site. The discussion includes key thermodynamic experiments, such as susceptibility and lattice constant, and spectroscopic experiments such as XPS and neutron scattering. This is followed by a review of existing theoretical work concerning both the ground states and the isomorphic phase transitions which occur in such compounds; the emphasis is on those aspects which make valence fluctuation phenomena such a challenging many-body problem.
707 citations
TL;DR: A review of the physical properties, composition and crystal structure of intermetallic compounds formed between rare-earth elements and non-magnetic metals, with emphasis on the magnetic properties is given in this article.
Abstract: A review is given of the physical properties, composition and crystal structure of intermetallic compounds formed between rare-earth elements and non-magnetic metals, with emphasis on the magnetic properties. Included are the properties of compounds in which the non-rare-earth component is a 4d or 5d transition element. Special consideration is given to the properties of pseudo-binary compounds. Results of magnetisation measurements, neutron diffraction and neutron scattering are discussed together with results derived from NMR, ESR and Mossbauer effect spectroscopy. An evaluation is given of the relevance of the experimental results with respect to different types of exchange interactions in this class of intermetallics. Special consideration is also given to the influence of crystal field effects on the magnetic properties and, furthermore, to the occurrence of intermediate valences in several of the compounds of Ce, Sm, Eu and Yb.
290 citations
TL;DR: In this paper, the authors report on the experimental work on dilute Pd-based alloys with Co, Fe and Mn and conclude that the giant moment should be accounted for by "normal" values of the magnetic quantum number (3/2 for Co, 2 for Fe and 5 2 for Mn) and a large value of geff.
Abstract: This paper is meant to be a report on the experimental work on dilute Pd-based alloys with Co, Fe and Mn. These alloys exhibit the phenomenon of giant moments. The importance of measurements on paramagnetic alloys is emphasized. From these measurements the conclusion can be drawn that Co and Fe dissolved in Pd does not behave like a normal paramagnet, i.e. according to a Brillouin function. This result makes it possible to explain the existing discrepancy in the interpretations of magnetic measurements on one hand and of specific-heat experiments on the other. The main conclusions of this paper are: The giant moment should be accounted for by ‘normal’ values of the magnetic quantum number (3/2 for Co, 2 for Fe and 5/2 for Mn) and a large value of geff. Paramagnetic alloys of Mn in Pd behave according to Brillouin functions, but alloys of Co or Fe in Pd do not. Hence, a number of interpretations of magnetic measurements should be considered as incorrect. The localized model for ferromagnetism can ...
206 citations
177 citations
TL;DR: In this article, the macroscopic and local properties of 3D transition metal impurities in normal metals are reviewed and compared with the theoretical situation in this field by inspecting the large body of experimental data of two typical alloys, which served as testing materials for the development of the existing theories.
Abstract: The macroscopic and local properties of 3d transition metal impurities in normal metals are reviewed and compared with the theoretical situation in this field. The parameters of the Anderson and s-d exchange models are derived from direct and indirect experimental data using as a guide the Hartree-Fock approximation of the non-degenerate Anderson model. The basic observations about the magnetic-non-magnetic transition, and the behaviour of the magnetic, thermal and transport properties when going through the transition region are demonstrated for specific examples. A detailed comparison between the present status of theory and experiment is performed by inspecting the large body of experimental data of two typical alloys, which served as testing materials for the development of the existing theories. CuFe is often regarded as a typical ‘yes moment’ system, and the experiments are therefore compared with the predictions based on the s-d exchange model; in the case of AlMn, the spin-fluctuation con...
109 citations
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TL;DR: In this article, the conditions necessary in metals for the presence or absence of localized moments on solute ions containing inner shell electrons are analyzed, and a self-consistent Hartree-Fock treatment is applied to show that there is a sharp transition between the magnetic state and the nonmagnetic state, depending on the density of states of free electrons, the $s\ensuremath{-}d$ admixture matrix elements, and the Coulomb correlation integral in the $d$ shell.
Abstract: The conditions necessary in metals for the presence or absence of localized moments on solute ions containing inner shell electrons are analyzed. A self-consistent Hartree-Fock treatment shows that there is a sharp transition between the magnetic state and the nonmagnetic state, depending on the density of states of free electrons, the $s\ensuremath{-}d$ admixture matrix elements, and the Coulomb correlation integral in the $d$ shell; that in the magnetic state the $d$ polarization can be reduced rather severely to nonintegral values, without appreciable free electron polarization because of a compensation effect; and that in the nonmagnetic state the virtual localized $d$ level tends to lie near the Fermi surface. It is emphasized that the condition for the magnetic state depends on the Coulomb (i.e., exchange self-energy) integral, and that the usual type of exchange alone is not large enough in $d$-shell ions to allow magnetic moments to be present. We show that the susceptibility and specific heat due to the inner shell electrons show strongly contrasting behavior even in the nonmagnetic state. A calculation including degenerate $d$ orbitals and $d\ensuremath{-}d$ exchange shows that the orbital angular momentum can be quenched, even when localized spin moments exist, and even on an isolated magnetic atom, by kinetic energy effects.
4,039 citations
TL;DR: In this article, the scattering probability of conduction electrons to the second Born approximatism was calculated based on the s-d interaction model for dilute magnetic alloys, and it was shown that J should be negative in alloys which show a resistance minimum.
Abstract: Based on the s-d interaction model for dilute magnetic alloys we have calculated the scattering probability of the conduction electrons to the second Born approximatism. Because of the dynamical character of the localized spin system, the Pauli principle should be taken into account in the intermediate states of the second order terms. Thus the effect of the Fermi sphere is involved in the scattering probability and gives rise to a singular term in the resistivity which involves clog T as a factor, where c is the concentration of impurity atoms. When combin:::d with the lattice resistivity, this gives rise to a resistance min~mum, provided the s-d exchan:~e integral J is negative. The temperature at which the minimum cccurs is proportional to c 15 and the depth of the minimum to c, as is observed. The predicted log T dependence is tested with available experiments and is confirmed. The value of J to have fit with experimmts is about -0.2 ev, which is of reasonable magnitude. Our conclusion is that J should be negative in alloys which show a resistance minimum. It is argued that the resistance minimum is a result of the sharp Fermi surface.
3,045 citations
01 Jan 1935
TL;DR: In this paper, the quantum mechanical method is applied to the theory of complex spectra and the Russell-Saunders case is used to obtain the energy levels of one-electron spectra.
Abstract: 1. Introduction 2. The quantum mechanical method 3. Angular momentum 4. The theory of radiation 5. One-electron spectra 6. The central-field approximation 7. The Russell-Saunders case: energy levels 8. The Russell-Saunders case: eigenfunctions 9. The Russell-Saunders case: line strengths 10. Coupling 11. Intermediate coupling 12. Transformations in the theory of complex spectra 13. Configurations containing almost closed shells. X-rays 14. Central fields 15. Configuration interaction 16. The Zeeman effect 17. The Stark effect 18. The nucleus in atomic spectra Appendix. Universal constants and natural atomic units.
2,607 citations